Thin bedded cherts and siliceous argillites of the Drook and Fresh Water Point Formations of the Conception Group were deposited above the wave base in most parts, as evident from the nature of bedding, large, scale ripple marks, penecontemporaneous deformation and calcareous nodules. The overlying Cape cove Formation of the same group is characterized by graded greywackes presumably deposited by turbidity currents. The animals that lived in the Conception sea during deposition of the Cape Cove Formation include pelagic as well as bottom dwellers. The presence of large-scale slump structures in the St. John's Formation
(St. John's Group) indicate a gently sloping surface of he depositional basin. The depositional environment of the St. John's Formation had become shallower than that of the underlying Conception Group.[TOP}

The geology of the Southeastern part of the Avalon Peninsula of Newfoundland has attracted a good deal of attention following the discovery of
the imprints of Late Precambrian Coelenterates (Anderson and Misra, 1968; Misra 1969a; 1969b) . The depositional environment of the rocks enclosing the imprints
can be studied on the basis of lithology, bedding characters and the sedimentary structures preserved in them.

The map area lies on the eastern part of a two sided Appalachian system
of Williams (1964) and its geology has been described by Misra (1969a; 1969b)
and Williams and King (1976). The age of the rock (Anderson and Misra, 1968;)
Anderson, 1972 is Precambrian. a short account of the stratigraphy and the
depositional history has been given by Misra (1971) and this paper is intended to deal with the ecological conditions in which
the animals lived and died in that basin.

The 3200 meter thick sequence of sedimentary rocks is separable into a
lower Conception Group consisting of banded cherts, green argillites, greywackes
and siltstones and an upper St. John's Formation of the Cabot Group (Rose, 1952;
McCartney , 1976; Misra, 1969b) comprising shales with sandstone laminae (Table
I, Figure 1). The Conception Group of the area was further subdivided (Misra,
1969a, 1971) into three formations: (1) Drook Formation, (2) Freshwater Point
Formation and (3) Cape Cove Formation, in the chronological order. Williams and
King (1976) have reclassified the rocks of the Conception Group into five
Formations which in the chronological order are: (1) Mall Bay, (2) Gaskiers, (3
Drook, (4) Briscal and (5) Mistaken Point. The first two formations are not
exposed in the map area and their stratigraphic position too is doubtful.
Williams and King (1976) themselves state that the Gaskiers and Mall Bay
Formations could be time equivalents of part of the Harbour Main Group. It is therefore preferable to take the base of the Conception Group at
the base of the Drook Formation and the Mall Bay and Gaskiers Formations can be
taken as part of the Harbour Main Group. The top of the Conception Group was
defined by Misra (1969a) at the transition from purple to grey beds. This criterion has been taken by Williams and King (1976) as well. They
have, however, subdivided the Cape Cove Formation into : (1) Briscal, (2)
Mistaken Point and (3) Trepassey Formations (Table I). Thus., the arbitrary
formational boundaries in the gradational succession may vary depending on the
parameters chosen but the sequence of depositional events will remain unchanged.

The
Drook Formation comprises a 1000 meter thick sequence of very hard, compact,
uniformly banded cherts and siliceous argillites. The most common constituents
as identified from X-Ray diffraction are quartz. albite, chlorite and sericite
(Table II). The secondary constituents are epidote, siderite and leucoxene.
Calcite is found only in the form of ellipsoidal, concretionary, flat-bottom
nodules (Fig. 6A of Misra, 1971). Large- scale current ripple marks are seen in
the exposures near Drook.
[TOP}

Overlying the Drook Formation with a gradational boundary are siliceous
and chloritic argillites and siltstones with minor proportions of medium to fine
grained greywackes similar in composition to the underlying Drook Formation
(Table II). The greywackes are composed of sub-angular to sub-rounded grains of
quartz, feldspar and rock fragments set in a matrix of chlorite, sericite,
epidote, leucosene and sphene. Syn-sedimentary floundering is locally indicated
by the ellipsoidal and other fragments in the siliceous argillites (Fig. 6C of
Misra, 1971) and pull aparts of sandstone layers within the argillites is also
seen.[TOP}

Overlying the Freshwater Point Formation with a gradational boundary is a
1200 meter thick sequence of uniformly graded greywackes, siltstones and
argillites. The proportion of greywackes in the graded units reaches a maximum
of about 60 per cent in the middle part of the formation; decreasing gradually
in the overlying beds. The graded units on their top surfaces near Mistaken
Point contain imprints or rich Precambrian fauna (Fig. 2A). The bottom of graded
units are characterized by load casts, flute casts, prod marks, groove casts and
graded bedding (Fig. 2C). The flute casts indicate the current direction towards
southwest and the prod marks taper out in a S30W direction.

Micrometric analysis shows that the sub-angular to subrounded quartz
(Fig. 3C) constitutes 2 to 38 per cent of the greywackes. Albite grains are
similar in shape

Table II. Variation in the proportion of quartz with respect to other
minerals in the argillites as determined by X-ray diffraction. Ratios
are based on peak lengths. Calcite has clearly developed
at the expense of quartz.

Formation

Sample No.

Q/A

Q/Chl.

Q/Cal

Chl./Seri

St. John's

MCR-26

3.25

3.40

-

1.55

"

MCR-18

3.25

3.25

-

1.78

"

MCR-2

1.99

2.36

3.20

1.90

"

MSH-4

2.61

3.65

1.58

1.59

Cape Cove

MCC-25

3.89

3.70

-

1.69

"

MLB-20

3.50

4.36

-

1.29

"

MLB-46

3.20

3.23

-

1.26

"

MFP-2

3.12

3.26

-

1.12

Freshwater Point

MCC-3

4.40

4.26

-

1.30

"

MPC-24

2.05

2.85

-

1.16

Drook

MPC-14

2.90

2.40

-

1.48

"

MPC-8

4.00

5.56

-

1.50

Note

A = Albite

Q = Quartz

Chl. = Chlorite

Cal. = Calcite

Seri. = Sericite

but smaller in size. Some plagioclase grains are sericitized and clouded. Rock
fragments are of chert, rhyolite, microgranite and basic volcanics. The matrix
constitutes 40 to 55 per cent of the greywackes and is composed of chlorite,
biotite, sphene, epidote, leucoxene, pyrite and rarely apatite.
[TOP}

The formation in the lower part comprises thin bedded, grey shales interstratified
with cross bedded sandy laminae (Fig. 2D), which in some cases are graded with
shale tops (Fig. 2F). The formation in its upper part is grey to dark grey
shales (Fig. 2E) with sandy streaks. Reduction in the thickness of beds compared
to those of the Conception Group indicates that the energy of the system had
decreased. The alternation of cross bedded with the graded units suggests that
turbidity currents were still in operation. Measurements on cross
stratification, sole markings and slumping King (1976) also suggest a transport
direction from northeast of the St. John's faults, slump breccia, slump nodules,
sand rolls produced as a result of contortion of beds. Convolute bedding (Fig.
3A) and other slump features are more common in the fine grained rocks. Some
other noteworthy features are alignment of minerals (fig. 3E) and cone-in-cone
structures observed on microscopic scale (Fig. 3F).

The rocks under microscope exhibit quartz, feldspar, mica, chlorite and
pyrite. The quartz grains in some calcareous sandstones gradually merge with
calcite in contacts, indicating an incomplete replacement of quartz by calcite.
The accessory minerals are normally the same as in the Conception argillites
(Fig. 3D) except that pyrite is more common and calcite more frequent. The
results obtained by X-ray diffraction of the shales reveal that illite and
montmorillonite are absent.[TOP}

Precambrian fossils occurring as imprints of jelly fish (near hammer
head), spindle shaped Hydrozoans and other forms, on the top surface of an
argillite bed in the Conception Group near Mistaken Point.

Siliceous argillites (light coloured) with intercalated sandy beds (dark
coloured) in the Fresh-water Point Formation. The irregular sandstone layer is
possibly the result of load casting.

2C.
Sharp contact between two consecutive graded units in the Cape Cove
Formation.

2D. Small - scale cross stratification overlying the shales in the basal part of the St. John's Formation.

2E.
Small-scale slump folds on a weathered surface of the shales in the St. John's Formation Pen for scale.

2F.
Interbeds of shale and sandstone in the basal part of the St. John's
Formation near Cape Race.

The
history of sedimentation requires the probable source of the sediments, their
transportaion and environment of deposition. The rock fragments and mineral
constituents of the rocks indicate that the sediments were derived from a
complex terrain consisting of volcanic, sedimentary and igneous rocks situated
to the northeast[TOP}

of the present exposures (Misra,
1971). Although the palaeogeography of the Avalon Peninsula of Newfoundland is
only vaguely known from the works of Rose (1952),

McCartney
(1967) and Brueckner (1969), the transport directions of the sediments indicate
an area of high relief to the northeast of the present exposures where from the
sediments were derived. The slope of the depositional basin as inferred from the
sole markings and slump structures was to the southwest.

Sedimentation of the Conception Group started probably in isolated basins
bound by volcanic rocks of the earlier Harbour Main Group. This situation
existed at least in the eastern part of the Avalon Peninsula and similar
isolated basins are envisaged by McCartney (1967) in the case of the sediments
that he included in the Harbour Main Group. These sediments assigned to the
Harbour Main Group are possibly the beginning of the Conception Group deposition
because locally the underlying volcanic rocks and Conception Group rocks are
interbedded in the transition zone. The rocks of the mall Bay Formation (williams
and King, 1976) reported from outside the area, seem to have this transitional
character. The glacial conditions represented by the tillites of the Gaskiers
Formation mark an important time plane (Anderson and Bruecknerm 1971) and may be
the cause of the extensive green
colour of the sediments.

The present study is confined to the rocks younger than the Gaskiers
Formation. The presence of limestone in the lower part of the Conception Group (Mccartney,
1967) and the calcareous nodules (Misra, 1971) indicate warm, clear water of
deposition. The presence of pillow basalt within the Drook Formation and a
proximal volcanic terrane (Williams and King, 1976) during the deposition of the
lower Conception Group suggest near shore conditions for the Drook Formation.
The other evidences of a shallow marine environment are penecontemporaneous
deformation, calcareous nodules, mega ripple marks, thixotropic deformation
(Misra, 1969a, 1971) and enormous silica precipitate. Even if it is conceded
that some of the silica beds are silicified siltstone, most of the siliceous
sediments (Fig. 5A of Misra, 1971) comprising a thickness of over 100 meters had
their origin in the underlying volcanic rocks of the Harbour Main Group. Uniform
parallel lamination in the cherts expressed by the colour bands suggests
tectonic stability.

The depositional framework of the Freshwater Point Formation was not much
different from that of the Drook Formation except that the influx of the
terrigenous sediments increased considerably towards the close of the formation.
A shallow water environment for the Freshwater Point Formation is inferred from
the type of lithology, bedding characters (Fig. 2B) and synsedimentary features
(Table I). In the upper part of the formation, graded bedding, grain size,
thickness of beds and lithology suggest that the energy of the depositional
system had increased. The environment of deposition gradually became deeper and
by the close of the deposition of the Freshwater Point Formation, the sea had
become deep enough for turbidity currents of large magnitude. This change in the
stability of the depositional basin corresponds with the Freshwater Point and
Cape Cove boundary and has possibly been taken by Williams and King (1976) as
the base of the Briscal Formation.

The rocks belonging to the Cape Cove formation were deposited by
turbidity currents in a basin whose northeasterly trending axis paralleled the
present strike of the beds. The main arguments in favour of this deduction are:

Absence of wave caused
disturbances,

Presence of sole marks including
flute casts (fig. 3B) and prod marks formed by unidirectional flow,

After a substantial thickness of the Cape Cove Formation was deposited,
the seaward slope upon the newly deposited detritus increased progressively.
During this period of progressive increase in the slope of the basin, submarine
slumping could have been initiated by agents like deep reaching wave action
during heavy storm, minor earthquakes, vulcanism (Misra, 1969a) or by abundant
supply of sediments during floods. Large-scale slump structures in the lower
part of the St. John's Formation (Misra, 1971) indicate that deposition was
taking place on a gently sloping surface. The laminated siltsones (Fig. 2F)
about 10 layers per foot, of
separate composition in the St. John's Formation indicate that the load was
carried by traction currents. Small-scale cross lamination (Fig. 2D) and cross
ripple laminations were formed by the currents having relatively high lutite
content and small amounts of large particles. The presence of pyrite (fig. 3E) and the grey colour of the sediments of the St. John's
Formation suggest that the depositional environment
was and the cone-in-cone structures (Fig. 3F) are of syn-diagenetic nature or
later.[TOP}

Within
the above frame work of the sedimentary basin and environmental condition, the
existence of the Precambrian animals of the Conception sea can be discussed .
Imprints of animals are found on the top surfaces of the graded beds in the
upper part of the Cape cove Formation (Mistaken Point Formation) and the
sediments enclosing them are of turbidite origin. The purple colour of the
sediments is characteristic and may indicate a humid tropical climate as
interpreted elsewhere by Wlaker (1974).

The animal imprints were grouped by Misra (1969b) into four categories:
(1) spindle-shaped organisms with bilateral symmetry (Fig. 2A), (2) leaf-shaped
organisms with stalk and hold-fast. (3) round lobate (jelly fish) forms (Fig.
2A) and dendrite like organisms. The fossils are believed to be the imprints of
soft-bodied Metazoans (Coelenterates and others) represented by Polyps as well
as Medusae. The Polyps include both colonial Hydrozoans and Pennatulid corals.
the round lobate organisms are jelly fishes and are represented by several
extinct species. The Mistaken Point and continue throughout the formation. In
most of the cases, they are covered by a thin film of volcanic tuff (Misra,
1969a,p. 102) suggesting that the volcanoes was responsible, at least partly,
for the death of the organisms. Since the fossils are found in a turbidite sequence of graded greywackes,
siltstones, and argillites containg load casts, flute casts, prod marks and
convolute bedding, the animals must have lived in a moderately deep environment
(Misra, 1969b). They were living probably at the bottom of the sea during the
intervening quiescent period between two successive turbidity currents and lived
until they were buried by sediments brought by suffocating turbidity currents.
Submarine volcanism was also an important cause of their death. In any case, the
surface of mud on top of the graded units provided the ideal conditions for
preserving the imprints.

Since the fossils are found only as impressions, no part of their body
preserved, it suggests that they were soft bodied Metazoans that constituted a
flourishing fauna during the Late Precambrian time in the Conception sea. The
fauna is supposed to be older than the Ediacara fauna of Australia. The fossils
are preserve in situ as
indicated by the preservation of the soft bodied animals in entirety. Besides,
the presence of bent or curled animal imprints and segmented forms in the fauna
together with the organisms with the hold fast (Misra, 1969b) are evidences of
their bottom dwelling habit.[TOP}

I
am grateful to late Prof. W.D. Brueckner of the Memorial University of
Newfoundland for financial assistance and guidance, to Prof. M.M. Anderson for
providing some of the recent literature and to Prof. K.S.Valdiya of Kumaun
University, Nainital, India for critical reading of this paper.
[TOP}